1. Field of the Invention
The present invention relates to a novel microporous consolidated material, or composite, and, more especially, to such novel composite comprising stacked fibers, including carbon fibers, deposited onto a perforated rigid substrate.
This invention also relates to a process for the production of such consolidated material and to various uses thereof, notably in the electrolysis of sodium chloride.
The microporous material according to the invention is especially useful for the manufacture of slab electrodes of the "glove finger" type, and for the production of microporous separators, such as diaphragms employed in electrolysis.
2. Description of the Prior Art
It is known to this art that microporous materials of the foregoing type should generally satisfy several requirements:
(1) They should have a microporosity which can be adjusted in terms of pore size and in terms of pore size distribution; PA0 (2) When they are used in the fabrication of the cathodic component of an electrolytic cell, such as for the electrolysis of sodium chloride, their thickness should be small : on the order of 0.1 mm to 5 mm, and they should have a large surface area which may exceed several m.sup.2. PA0 (i) of the fibrous materials in suspension; PA0 (ii) of the surfactants and various additives incorporated therein; PA0 (iii) of the pore-forming agents incorporated therein. PA0 (i) a perforated, rigid support substrate which may define an elementary cathode having one or more planar face surfaces, or face surfaces in the form of cylinders deemed "glove fingers", thus providing an open surface; and PA0 (ii) a fibrous structure deposited-therein which comprises the carbon fibers according to the invention, if required in combination with other fibers such as asbestos fibers, advantageously consolidated with binders such as polymeric binders, themselves advantageously comprised of fluorinated polymers.
Additionally, it should be possible to prepare these microporous materials by deposition onto a rigid base structure which has a great number of apertures or perforations and large perforation or hole diameters.
These microporous materials are typically produced by filtration of a suspension of fibers and binders onto the support under vacuum.
The properties of such a material depend upon a certain number of parameters, especially on the nature and the concentration:
According to the prior art, a fibrous material having a polydisperse distribution of fiber lengths, i.e., a broad spectrum of fiber sizes and lengths, is employed. Thus, at the beginning of the deposition of the fibrous material, the long fibers form a kind of first layer which then arrests or stops the shorter fibers from penetrating therein. A high level of prevention of fibrous materials is thus obtained; unfortunately, often at the expense of the quality of the microporous material. The latter, especially in the case of use for electrolysis, should be of small thickness; moreover, it should be regular.
Furthermore, it too is known to this art that the concentration of fibrous material should not fall below a certain minimum value at the time of deposition. Otherwise, the homogeneity and the stability of the suspension are adversely affected.
Stated differently, in order to obtain good deposition, the content in fibrous material per unit volume must not change during the filtration process. This is a critical point.
Hence, this art has long been the subject of attempts to improve the quality of the suspension by varying the parameters mentioned above, viz., the nature and the concentration of the fibrous materials, of the surfactants and additives, and of the pore-forming agents.
But it is also known that the possibilities in this direction are limited by the constraints related to the characteristics of the microporous materials, especially those which are imposed by their use in electrolysis.
Finally, with a view to producing microporous materials which perform at higher levels and which are more profitable from an economic point of view, the present inventors have heretofore proposed microporous materials containing conductive fibers, such as carbon or graphite fibers.